Sphalerite: Gemstones Information
Sphalerite is (Zn,Fe)S and forms tetrahedral, dodecahedral, often complex transparent to translucent colourless to yellow, red, green and brown crystals of the cubic system with resinous to adamantine lustre, perfect dodecahedral cleavage, hardness 3.5–4 and SG 3.9–4.1. The RI is 2.37–2.43 and the dispersion notably high at 0.156. Some specimens fluoresce a bright orange-red to red under both forms of UV. Sphalerite occurs in a variety of hydrothermal conditions and is the chief ore of zinc. Very fine material comes from Picos de Europa, Santander, Satander Province, Spain, and near-colourless to pale green crystals from Franklin,New Jersey, USA. Some crystals show absorption bands in the red; the strongest and clearest is at 665 nm and a much weaker one is at 651 nm.A fairly strong broad band is centred near 692 nm. A red filter serves to diminish the glare from the yellow part of the spectrum, assisting observation of this band. Cadmium may be the cause.